Reference signals may generally be classified into two types: one type is used for measuring a channel state or measuring channel quality, so as to implement scheduling; the other type is used for performing coherent demodulation on a receive signal including control information or data information. For example, a reference signal used for coherent demodulation is referred to as a demodulation reference signal (DMRS), and the reference signal is also referred to as a user equipment (UE)-specific reference signal (UE-specific reference signal), and is used for performing channel estimation when a physical downlink shared channel (PDSCH) is demodulated; a reference signal used for measuring channel state information is referred to as a channel state information reference signal (CSI-RS), which is especially used in a situation in which multi-antenna transmission is performed. A rank indicator (RI), a pre-coding matrix indicator (PMI), a channel quality indicator (CQI), and other feedback information may be derived from channel measurement based on a CSI-RS. A cell specific reference signal (CRS) may be used for UE channel estimation, so as to implement demodulation of a physical downlink control channel (PDCCH) and another common channel. In addition, the CRS may be further used for measuring signal quality, such as reference signal received power (RSRP) and reference signal received quality (RSRQ), so as to implement a function such as cell selection.
Multiple antennas are widely used in a modern communications system, so as to increase capacity and coverage of a system or improve user experience. For example, a Long Term Evolution (LTE) R8 system can support four antenna ports, and LTE R10 to R11 systems can support eight antenna ports. Each antenna port may correspond to one physical antenna or one virtual antenna, where the virtual antenna is a weighted combination of multiple physical antennas. The communications system may obtain channel estimation associated with each antenna port by using a pilot signal or a reference signal.
In order to further improve spectral efficiency, more antenna configurations, such as an antenna configuration based on an active antenna system (AAS), are introduced. An AAS base station further provides a vertical design of a freedom degree of an antenna, and therefore, the AAS base station can be implemented by using horizontal and vertical two-dimensional antenna arrays thereof. For the AAS base station, even though quantities of antenna ports are the same, antenna array structures may be different. For example, sixteen antenna ports may be implemented by using a 2×8 antenna array, or may be implemented by using a 4×4 antenna array. Therefore, for antenna ports having same numbers, different channel state measurements may also be obtained in different array structures.
In the prior art, multiple solutions for acquiring a transmit antenna port quantity configuration are provided. However, because information about the configuration is actually specific to a design of a horizontal antenna array, the information about the configuration cannot adapt to an antenna array structure of the AAS. In addition, an existing system can only support a configuration of eight antenna ports at most. That is, the prior art cannot implement an adaptive configuration of an antenna array structure of the AAS, and cannot support a reference signal configuration of more than eight antenna ports.